A conventional constant-modulus alloy having high Young's modulus, and a low temperature coefficient of Young's modulus is based on Fe—Co—Ni—Cr—Mo—W. Such an alloy is used for a hair spring, which in turn is used for a mechanical driving apparatus, which in turn is used for a watch and clock.
Patent Document 1: Japanese Examined Patent Publication (kokoku) No. 31-10507 relates to an Fe—Co—Ni—Cr—Mo—W-based constant-modulus alloy having a composition mainly composed of 8 to 68% Fe, 1 to 75% Co, 0.1 to 50% Ni and 0.01 to 20% Cr, all by weight, and further containing 2 to 20% W and 2 to 20% Mo. However, the present inventors' research revealed that only a partial compositional range of said alloy provides a temperature coefficient of Young's modulus in a range of (−5˜+5)×10−5 degrees C.−1 and saturation magnetic flux density in a range of 2500 to 3500 G. The coefficient of linear expansion and temperature coefficient of elastic modulus were measured but magnetic properties were not measured in Patent Document 1. The production method is described as follows. Molten alloy is cast, an ingot is forged, and wiredrawing or rolling is carried out. Depending on the application of the alloy, wiredrawing or rolling temperature is selected at either ordinary temperature or high temperature. The resultant alloy having a predetermined shape is annealed at 500 to 1100 degrees C., followed by slow cooling. Alternatively, subsequent to the annealing, working at ordinary temperature may be carried out, followed by heating at 750 degrees C. or lower and then slow cooling. In addition to and/or instead of the above process, the ingot may be quenched from a high temperature. An intermediate heat-treatment after wiredrawing is not described.
Non-patent Document 1, “Anisotropy and its temperature dependence of elastic modulus for a single crystal of high elastic alloy,” Bulletin of Japan Institute Society for Meals., Vol. 31, No. 3 (1967), pages 263-268, measures anisotropy of elastic modulus of a crystal, which has a composition (wt %) of 22.4% Fe, 38.0% Co, 16.5% Ni, 12.0% Cr, 4.0% Mo, 4.0% W, 1.2% Mn, 1.0% Ti and 0.8% Si. This composition falls within the compositional range of Patent Document 1. Dia-flex has a “high” elastic modulus and is used as a mainspring but is not a constant-modulus alloy.
Generally, a single crystalline alloy having a face centered cubic lattice has the following relationship of Young's modulus in <100> direction E<100>, Young's modulus in <110> direction E<110>, and Young's modulus in <111> direction E<111>.E<100><E<110><E<111>As is described in Non-patent Document 1, E<111> of Fe—Co—Ni—Cr—Mo—W based alloy is approximately three times as high as E<100>. Among the crystal orientations of a face center cubic lattice alloy, Young's modulus is the highest in <111> orientation. However, constant modulus property is not attained in a single crystalline multi-component alloy having a face centered cubic lattice. In addition, Non-patent Document 1 describes that high elasticity alloys used at present for a commercial mainspring are principally oriented to {110}<112>, which direction is of low Young's modulus. Meanwhile, the relationship between the texture and constant modulus property is not elucidated for a polycrystalline multi-component alloy having a face centered cubic lattice.
FIG. 1 shows the relationship between Young's modulus and measurement temperature for Alloy No. I (comparative example), Alloy No. II (comparative example) and alloy No. 12. The wires drawn at a working ratio of 85.3% were subsequently rolled at a rolling reduction of 50%. The resultant sheets were heated at 650 degrees C. for 2 hours. Note that an intermediate heat treatment is not performed between wiredrawing steps of these alloys. Alloy No. I, which is a commercially available constant-modulus alloy (a registered trademark Elcolloy is owned by one of the present applicants), has a composition of Fe—27.7% Co—15.0% Ni—5.3% Cr—4.0% Mo. Sheet-like samples of respective alloys exhibit relationships between Young's modulus and measurement temperature as shown in FIG. 1. Young's modulus has a flat region in the vicinity of room temperature, that is, 0 to 40 degrees C., where elasticity is constant. Such an alloy is shaped into a hair spring and is mounted in a mechanical driving apparatus, which in turn is used in a watch and clock. Magnetic transforming point of this alloy is 200 degrees C. and is positioned in a vicinity of the peak of a Young's-modulus temperature-dependent curve. This alloy is ferromagnetic and has a saturation magnetic flux density of as high as 8100 G. Therefore, this alloy involves a drawback that it is easily magnetized in an external magnetic field described in detail hereinafter.